OBJECTIVE: To assess the effect of growth and aging upon bone metabolism in rhesus monkeys. RESULTS Old world monkeys are often used as models for skeletal development and aging however, the age of peak bone mass and the effect of advancing age is not well known. The aim of this study was to use DXA and measurements of bone metabolism to more clearly characterize skeletal development and aging in rhesus monkeys making them better understood models for osteoporosis and aging research. Sixty female and 56 male rhesus monkeys (4-34 yr.-) were studied for the above endpoints. Peak bone mass was achieved by approximately 10 yrs. of age in both groups. In males, there was a significant decline (p<0.001) with age (based on regression analysis) in bone mineral content (BMC) and density (BMD) of the lateral lumbar spine, femur and distal radius. In addition, bone turnover decreased with age. Using endocrine data and menstrual cyclicity, females were divided into 3 groups, growing (G, n=12), adult (A, n=31) and old (O, n=17). O animals were lower (p<0.05) than A animals in total body BMC, anterior-posterior spine BMD and proximal radius BMC and BMD. Osteocalcin, 25-hydroxyvitamin D and calcium levels were also significantly (p<0.05) lower in O compared to A animals. In addition, lumbar spine radiographs were taken to adjust for the effect of osteoarthritis on measurements of BMC and BMD. In males and females, there was a significant (p<0.001) increase in the incidence of spinal osteoarthritis with age. FUTURE DIRECTIONS We plan to continue using DXA, radiographs and markers of bone metabolism to better characterize the skeletal aging process in rhesus monkeys making them better understood models for osteoporosis research. KEY WORDS Osteoporosis, bone density, aging, bone metabolism, DXA